#define _CRT_SECURE_NO_WARNINGS 1
#include <iostream>
using namespace std;

int getSum(int n);

int main() {

    int n;
    cin >> n;

    cout << getSum(n) << endl;

    return 0;
}

int getSum(int n) {

    // write your code here......
    if (n == 1) return 1;
    int arr[21];
    arr[0] = 0;
    arr[1] = 1;
    arr[2] = 1;
    for (int i = 3; i <= n; i++) {
        arr[i] = arr[i - 1] + arr[i - 2];
    }
    return arr[n];
}

